The only thing needed is to install a free app from your phone's app store (I recommend Mobilevoip or phone2phone, there are others), load some prepaid credit and you can start calling.
But anyway, what you are describing doesn't concern the usual prepaid roaming user who already went through the trouble of ordering a prepaid SIM from the Internet, as it is even easier to get the app from the phone's app store than it is to order a SIM from some website.
Not at all. It cost 0.09£/min to call.
As I said, today carriers are replacing the old home phones with SIP phones all over the world. And once you have a SIP phone you add any cheap provider you want.
And these cheap providers also offer landline numbers in the major countries. I.ex: you call the UK landline and then you dial the number you want, i.ex: 0.09£ to call the +372 mobile (or free to call the +1 Toggle number, 0.005 to UK Toggle number).
It's so easy, stop looking for excuses to pay more. But if you prefer to pay more, please do so.
If your friends prefer to stop calling you because they prefer to keep calling with their outrageously expensive operators, I think it's better to look for some new friends. But that's just my opinion.
And BTW, calling your friends back after they ring you comes out cheaper for you than using Piranha to receive the call. (for convenience
and worldwide coverage I am assuming a dual-SIM phone setup with Toggle + AnyTravelsim with betamax callback).
I use the betamax providers. They have been working great for the past 10 years.
They have nothing to do with the SIM. I even recommend to setup the home landline phone with this, as it is much cheaper than anything else.
Minimum top up is 10$.
Rates here:
http://progx.ch/home-voip-prixbetamax-3-1-2.html
They allow callback, local access numbers, SIP and VOIP.
You can set any caller ID you want. So, for example, if you set your Mobile number as caller ID people don't even know you aren't calling directly with your phone.